This proposal outlines the development of a minimally invasive cardiac output (CO) monitor for routine use for pediatric and neonatal patients in the intensive care unit setting. Presently, no technology is available for this use. Preliminary results using a prototype system in bench, animal, and in clinical trials demonstrated the potential accuracy and usefulness of this technology. The methodology presents the advantages of requiring only arterial and central venous access (no cardiac catheterization involve), use of innocuous isotonic saline as an indicator, no contact with the patients blood, and minimized indicator volumes administered to the patient. This method also provides the additional diagnostic information of septal defect identification and measurement of the blood volume in the heart, lungs, and great vessels. The objectives of this proposal are to develop new sensors to increase the capabilities of the system, to expand the data archive of CO dilution curves, to expand the use of the device to neonatal patients, to validate the system against thermodilution CO measurements, and to develop hardware that incorporates automatic control of a syringe pump that is used in the measurement.